Trouble is that the bolt is around four inches long and is actually stuck in the back end of the trigger block
If heat is applied to the trigger block, It should expand it- Hopefully less than it expands the bolt, This way it could loosen it's grip on the bolt..
I just tried a 12" bronze 1/2" dia rod down it, Tapped it on the head of the bolt and it's actually loosened ever so slightly, Strange thing is that when I tight it, It becomes loose,
If I undo it by the 10° or so, It grips the stock better!!
John